I'm having the same issue. I have the same engine/magneto setup. I don't have a lighting coil so I'm trying to figure out what to do with the other end of the source coil. One end goes to the condenser and the other end in diagrams show it going to the lighting coil.. which as stated above - I do not have. Do I just ground it or what? Help would be greatly appreciated! Also what is the part number on your stator plate? Mine is FOTO19 - or something like that. I know it says 19. Thanks ahead of time!

ZCDCDT assuming yours is a 75 DT250B you do have the correct stator plate FOT0109 (Mitsubishi). The wire that 'linked' over from your ignition source coil to the lighting coil needs to earthed. Make sure you scrape ALL the brown resin insulation off the end of the wire and then solder an eyelet connection to it. Use the source coil locating screw to provide the path down to earth.
Regarding the lighting coil you said you don't need (cause all the 3 wires are taped off elsewhere on the bike) from a mechanical engineering aspect I would still leave it in position. Although it has no electrical-loads attached from the charging or lighting circuits there is still the magnetic interaction between the coil and the rotating magnets which represents a rotational force.  Leaving in situ helps balance out the 180 deg opposite force created by the source coil. Hope this helps, Andy.

Post #11. Just my ideas so up to you, but--you say you 'don't have a lighting coil' so yes just earth the ignition source & she'll run. For some reason they used to earth the source coil through the lighting coil. I've yet to work out why. But 50 years ago at work when a DT1 came in misfiring & lights were fluctuating, it turned out the lighting windings were jangling around on their pole. As the customer wasn't worried about lights in this case i just earthed the source separately. Think the lights just carried on the same anyway as that coil has its own earth to the mount screw. Be interesting to understand yamaha's electrical reasoning for doing 'that'. Does it magically boost the spark by involving some of the lighting windings--i dunno. I do know though that if the points are a bit grubby or fractionally wide plus dirty & the bike is running good but turn the lights on & it makes the ignition play up unless you clean & gap the points. I've got 3 bikes with the 'source coil only' on the plate, a 360 a 280 & a 250 & they all work as intended. Electrics are a good subject for discussion--'arguments, bit like an oil thread haha., ps, i can see it'd be a good idea in theory to have an unwound coil pole in the empty space although i've not done that on mine--should i be worried.

See here is the thing. I've had to locate these parts individually. I should also know that I do not have the bike, just the engine. I don't know where the taped off comments came from, I don't have anything taped off everything is soldered. I've only got one wire coming out of the stator compartment. I started with case halves and have been purchasing parts where I can find them at discount. Being on a budget I did not purchase the lighting coil because I will be using the engine in either a small quad or my 1972 cb175 motorcycle. My Cb 175 engine needs a valve job and being a two-stroke enthusiast I'd rather do an engine swap then send the CB head out to have the valves done. 

I'm close here. I have everything for this 75 dt250 engine now together, from the exhaust to the autolube, new carb, new source coil and new points and condenser. Like I said I did not see the point in buying the lighting coil because at least for right now I just want to see if I can get this engine started.

Good to know I have the correct stator plate. My last concern is that the coil I bought only fits on the right side of the stator plate. From everything I see from manuals the source coil is located on the left. I was sure that I ordered a New Old stock source coil for a 75 dt250b but when I got it it did not fit in the left spot of the stator plate. However for some reason it fit perfectly on the right side. I'm sure it is a source coil and not a lighting or charging coil. It has thinner laminated wire and when I do an ohm reading across the coil I get 1.6 ohms. Question being will this still work if it is on the right side of the stator plate? Or will this set up not work?

Anyone who feels they can answer this for me please do! I'll provide a picture too if anyone is confused.
By the way thank you for the quick reply last night!

Hello ZCDCDT, it’s Andy again from the UK.  Apologies for the confusion I caused with my post regarding the “wires being taped off on your lighting coil”.  I did edit my original post to include Doug Shinault (Curly) next to your name but for some reason the edit didn’t work.  You see it was his lighting coil wires that had been taped off.   Anyway, RT325 correctly mentioned about the possible reasoning behind Yamaha linking the source coil to a few of the lighting coil windings before taking both down to a common earth.  I remember a Technician at Rex’s speedshop telling me it was indeed to give the source coil a bit of extra ‘boost’ i.e. peak voltage.  This leads on to your technical question about will your purchased source coil work on the RHS of the stator plate.  My initial thoughts were no it almost certainly won’t because the positioning of the source coil relative to the magnetic flux ensures that when the ‘points’ open the AC sine wave voltage is at a peak (i.e. max voltage) to give a nice fat spark.  BUT on re-thinking how the lighting coil example above boosted the source coil volts, this happened because the lighting coil is 180 deg opposite the source coil so it is also at a peak voltage point on the typical sine wave.  Therefore in theory positioning the source coil where your lighting coil was, might just work..!!  I wish I could give you a more definite answer on this matter but it could come down to simply giving it a try.  Not too much work involved really as it would only require you to fit the coil (make sure it’s earthed) fit the flywheel, set the points, hot wire the condenser black wire direct to the ignition coil LV connector, crank the engine with the kick start lever whilst holding the spark plug to the cylinder fins.  Good luck and hope this helps this time, Andy.

Thank you so much for that detailed response! I got it all set up including grounding the end of the source coil. I've been trying for like an hour to set the points but I don't see any deviation from where I set the points to any other spot around the rotation of the flywheel meaning the points are not opening or closing. I am looking at the flywheel and am trying to see where this lobe would be but I'm just not seeing it I took my digital calipers and measured around the outside taper shaft and I seem to be getting the same number all the way around. I then looked at the flywheel number and it reads f o t o 2173. Something tells me I have the wrong flywheel even though it does fit on the taper shaft perfectly and fits around the magneto just fine. Something tells me I'm going to have to buy another flywheel. Can anyone confirm this for me? My guess is that this flywheel is set up for a CDI?
Could I use this flywheel and go with a pickup and CDI coil? Has anyone ever tried using a Yamaha blaster source coil and pick up and cdi? The Yamaha blaster is a four magnet CDI setup. If the blaster source coil fit on this magneto plate could that work?

Does anyone have the appropriate flywheel and willing to trade? This is the second time now I've bought the wrong flywheel. I'd be willing to trade all my coils and both fly wheels for the right flywheel LOL

Thank you so much for that detailed response! I got it all set up including grounding the end of the source coil. I've been trying for like an hour to set the points but I don't see any deviation from where I set the points to any other spot around the rotation of the flywheel meaning the points are not opening or closing. I am looking at the flywheel and am trying to see where this lobe would be but I'm just not seeing it I took my digital calipers and measured around the outside taper shaft and I seem to be getting the same number all the way around. I then looked at the flywheel number and it reads f o t o 2173. Something tells me I have the wrong flywheel even though it does fit on the taper shaft perfectly and fits around the magneto just fine. Something tells me I'm going to have to buy another flywheel. Can anyone confirm this for me? My guess is that this flywheel is set up for a CDI?
Could I use this flywheel and go with a pickup and CDI coil? Has anyone ever tried using a Yamaha blaster source coil and pick up and cdi? The Yamaha blaster is a four magnet CDI setup. If the blaster source coil fit on this magneto plate could that work?

Does anyone have the appropriate flywheel and willing to trade? This is the second time now I've bought the wrong flywheel. I'd be willing to trade all my coils and both fly wheels for the right flywheel LOL

Andy L is a bit more advanced on electrics than my methods of "try it & see" lol & love reading his posts. But i would have thought it'd work. Now it looks like you have a cdi flywheel. Cam is plain to see although doesn't have 'much lift'. Probably easier to buy a flywheel in the end as sounds like you're 'that close' to running. I've done some tricks that worked over the years. One being on a DT125 watercooled trail. Lighting coil screws came out & stuffed that coil plus the trigger coil. So source coil was ok 'just', so i had a cdi box secondary ":plug" coil combined of an RG50, JR50, common small suzuki setup. So no trigger required. Just one wire from the source to the one connection up top. Sparked so strobed it with "wife turning back wheel in gear up on the stand haha" & timing looked good. Thought i might need to time it minus the crank key but 'no', which was good. Anyway--ran perfect & kids used it for a long time until i sold it. So, probably not worth doing in your case but if ya wanted to you'd need a source with about 350 ohms resistance & a combined secondary coil with cdi box. Love other peoples projects & hope we see some pics of it oneday. DT250 in a CB175 sounds like fun!!. Exhaust port run into the front down tube?. Cheers. ps, i'm in NZ so all sorts of dodgy stuff going on to keep thing running as parts are scarce & damn expensive.Last trick like yours was my RD200 in a PE250, made twin chamber highup exhaust & ran good--sounded great. That was about 35 years ago. Have an XL185 in it now.